|Preheat oven to 350°. Lightly coat a 1-1/2 quart casserole with non-stick cooking spray and set aside.
In a large, heavy saucepan over medium heat, heat water and oil until bubbling. Stir in flour, Cayenne and mustard. Stir frequently with a wire whisk for 3 minutes (sauce may lump at this stage.) Over the course of 5-7 minutes, add hot milk, whisking constantly (sauce should continue bubbling as you add the milk, or you're adding the milk too quickly.) If necessary, after all the milk is added, continue to cook for about 2-4 minutes, until the sauce is the consistency of thick cream.
Season with salt and pepper to taste. Remove from heat and stir in 1/4 cup of the cheddar cheese and all the Swiss cheese.
Pour macaroni into a prepared casserole and top with the sauce and toss well to coat all the macaroni.
Sprinkle remaining 1/4 cup cheddar and breadcrumbs on top, bake for 30 minutes or until lightly browned and bubbly.